I am a professor of Medieval literature and as such have come in contact with seige engines; however, I've never tried to build one. As a hands-on class project this semester, one of my classes wants to build a half scale trebuchet, a catapult big enough to fling a ten-pound watermelon over the student union. The projectile will need to travel roughly 60 yards and reach a height of 30 feet. Does anyone know of primary or secondary sources which detail the building of seige engines? If anyone can provide me with a bibliography of designs or plans for such a catapult, I and my class will be ever so grateful.